1. Field of the Invention
Aspects of the present invention relate to an image forming device capable of controlling a scanning unit and a method to control the scanning unit thereof. More particularly, aspects of the present invention relate to an image forming device capable of controlling a scanning unit so as to enhance control of positioning a motor by calculating a position error as well as a rate error of the motor which drives the scanning unit and adjusting accordingly, and a method to control the scanning unit thereof.
2. Description of the Related Art
In general, devices using a direct current (DC) motor control the rotation rate and rotation position of the DC motor with two pulses output from an encoder. In more detail, conventional image forming devices capable of controlling a scanning unit measure the practical rotation rate of the motor using a time interval between the two pulses output from the encoder. Additionally, the conventional image forming devices indirectly acquire a rotation position of the motor by counting falling edges or rising edges generated from the two pulses output from the encoder. Accordingly, the conventional image forming devices are limited in controlling the motor to be positioned at a particular position at a particular time by moving at a regular rate.
FIG. 1A is a graph showing a moving distance (i.e., a rotation position of the motor detected by a conventional image forming device), and FIG. 1B is a graph showing a position error generated by Pcmd and Pmea of FIG. 1A. In FIGS. 1A and 1B, Pcmd is the target rotation position of the motor, Pmea is the practical rotation position of the motor, Perr is the error between Pcmd and Pmea, and t is the time. FIGS. 1A and 1B show that there is an error between the practical rotation position and target rotation position of the motor.
If such a conventional image forming device capable of controlling a scanning unit is mounted in a scanner, a Charge-Coupled device (CCD) that is driven by a DC motor has an irregular moving distance and a scanned image is distorted.